Single Polarization State Research Articles

Coupling strength comparison in optical fiber with multiple sector shape stress elements

AbstractThe maximum stress oscillation amplitude and maximum coupling strength of the optical fiber with multiple sector stress elements are studied. Optimized fiber structure with craft feasible is designed and the related structural parameters are given. Comparing the research results, it is found that the optical fiber with triple sector stress elements can achieve the strongest coupling strength to realize the single circular polarization state conversion by the shortest coupling distance. In addition, though the maximum coupling strength is decreased as the number of stress elements increases, it remains the same order of magnitude as the triple sector's. So from the craft perspective, whether it is an optical fiber with triple sector stress elements or the other optical fiber with more sector stress elements, the optical fiber with the property of single circular polarization transmission can be achieved if the spinning rate satisfies the phase matching condition.

Functionally switchable terahertz metasurface under linearly polarized and circularly polarized waves incidence

Currently, most reported terahertz metasurfaces can only respond to terahertz waves with a single polarization state (linearly polarized or circularly polarized wave), which poses a problem of limited degrees of freedom in regulation. Facing this challenging issue, we design a functionally switchable terahertz metasurface that can achieve independent control of linearly polarized and circularly polarized terahertz waves. It comprises a top layer photosensitive silicon and metal composite structure, a middle polyimide medium, and a bottom layer metal plate. By changing the conductivity of photosensitive silicon, the same metasurface structure can achieve two different functional mode switching under different polarization wave incidences, such as switching between beam splitting and vortex beam, switching between RCS and multi vortex beams, switching between single focus and multi focus. This structure provides a new idea for the flexible regulation of terahertz waves.

Switchable and tunable orthogonal single-polarization dual wavelength SLM fiber laser based on parity-time symmetric system and PM-FBG

A dual-wavelength narrow linewidth orthogonal single polarization fiber laser based on a parity-time (PT) symmetric system is proposed and demonstrated, which achieves the function of tunable and switchable wavelength, and single longitudinal mode (SLM) operation. The PT symmetric system composes of a single physical loop, which includes two polarization controllers (PCs) and a polarization beam splitter (PBS). By modulating PCs to match gain, loss and coupling coefficient, the switchable wavelength and stable SLM laser output have been achieved. Through stretching the polarization maintaining fiber Bragg grating (PM-FBG), the wavelength adjustment range from 1549 nm to 1551 nm is obtained. In the process of tuning, the full width at half maxima (FWHM) linewidths and polarization states at each wavelength have been measured and keep basically stable. The measured FWHM linewidths are less than 13.66 kHz and 11.89 kHz. Further, the stable orthogonal single polarization state has been realized. The degree of polarization (DOP) at each wavelength exceeds 97% and basically remains unchanged during 20 min.

Single-input polarization-sensitive optical coherence tomography through a catheter.

Intravascular polarimetry with catheter-based polarization-sensitive optical coherence tomography (PS-OCT) complements the high-resolution structural tomograms of OCT with morphological contrast available through polarimetry. Its clinical translation has been complicated by the need for modification of conventional OCT hardware to enable polarimetric measurements. Here, we present a signal processing method to reconstruct the polarization properties of tissue from measurements with a single input polarization state, bypassing the need for modulation or multiplexing of input states. Our method relies on a polarization symmetry intrinsic to round-trip measurements and uses the residual spectral variation of the polarization states incident on the tissue to avoid measurement ambiguities. We demonstrate depth-resolved birefringence and optic axis orientation maps reconstructed from in-vivo data of human coronary arteries. We validate our method through comparison with conventional dual-input state measurements and find a mean cumulative retardance error of 13.2deg without observable bias. The 95% limit of agreement between depth-resolved birefringence is 2.80 · 10-4, which is less than the agreement between two repeat pullbacks of conventional PS-OCT (3.14 · 10-4), indicating that the two methods can be used interchangeably. The hardware simplification arising from using a single input state may be decisive in realizing the potential of polarimetric measurements for assessing coronary atherosclerosis in clinical practice.

Multi-Level Logarithmic Amplification-Based Fixed Threshold Circular Polarized On-Off Keying Detection for Free-Space Optical Communications

This study investigates a multi-level logarithmic amplification (MLA)-based fixed threshold circular polarized on-off keying (CP-OOK) detection for free-space optical (FSO) communication links. OOK signal is polarized into a single circular polarization state by a linear polarizer (LP) and a quarter-wave plate (QWP). In the receiver terminal, firstly, circular polarization is transformed into linear polarization utilizing QWP without polarization coordinates alignment between transmitter and receiver. Then, the background noises are decreased by polarization filtering using LP. Then, CP-OOK signal intensity variation is eliminated by nonlinear gains from MLAs in the low gain nonlinearity condition. Finally, fixed threshold decision (FTD) is realized by optimizing cascaded LAs to reduce the extinction ratio distortion of the CP-OOK signal. The proposed CP-OOK transmission is analyzed under various strengths of turbulence channel and different configurations of MLAs. Simulation results demonstrated that the proposed CP-OOK signal was effectively detected by FTD with optimized MLAs.

Six-channel programmable coding metasurface simultaneously for orthogonal circular and linear polarizations

Metasurfaces have intrigued long-standing research interests and developed multitudinous compelling applications owing to their unprecedented capability for manipulating electromagnetic waves, and the emerging programmable coding metasurfaces (PCMs) provide a real-time reconfigurable platform to dynamically implement customized functions. Nevertheless, most existing PCMs can only act on the single polarization state or perform in the limited polarization channel, which immensely restricts their practical application in multitask intelligent metadevices. Herein, an appealing strategy of the PCM is proposed to realize tunable functions in co-polarized reflection channels of orthogonal circularly polarized waves and in co-polarized and cross-polarized reflection channels of orthogonal linearly polarized waves from 9.0 to 10.5 GHz. In the above six channels, the spin-decoupled programmable meta-atom can achieve high-efficiency reflection and 1-bit digital phase modulation by selecting the specific ON/OFF states of two diodes, and the phase coding sequence of the PCM is dynamically regulated by the field-programmable gate array to generate the desired function. A proof-of-concept prototype is constructed to verify the feasibility of our methodology, and numerous simulation and experimental results are in excellent agreement with the theoretical predictions. This inspiring design opens a new avenue for constructing intelligent metasurfaces with higher serviceability and flexibility, and has tremendous application potential in communication, sensing, and other multifunctional smart metadevices.

Dynamically Tunable and Multifunctional Polarization Beam Splitters Based on Graphene Metasurfaces.

Based on coupled-mode theory (CMT) and the finite-difference time-domain (FDTD) approach, we propose a graphene metasurface-based and multifunctional polarization beam splitter that is dynamically tunable. The structure, comprising two graphene strips at the top and bottom and four triangular graphene blocks in the center layer, can achieve triple plasma-induced transparency (PIT). In a single polarization state, the computational results reveal that synchronous or asynchronous six-mode electro-optical switching modulation may be performed by modifying the Fermi levels of graphene, with a maximum modulation degree of amplitude (MDA) of 97.6% at 5.148 THz. In addition, by varying the polarization angle, a polarization-sensitive, tunable polarization beam splitter (PBS) with an extinction ratio and insertion loss of 19.6 dB and 0.35 dB at 6.143 THz, respectively, and a frequency modulation degree of 25.2% was realized. Combining PIT with polarization sensitivity provides a viable platform and concept for developing graphene metasurface-based multifunctional and tunable polarization devices.

Improving long-term temperature bias stability of an integrated optical gyroscope employing a Si3N4 resonator

The presence of polarization noise generated by the waveguide resonator limits the performance of a resonant integrated optical gyroscope (RIOG). Using silicon nitride ( Si 3 N 4 ) to fabricate a waveguide with an ultralow-aspect-ratio can result in a resonator that only supports light transmission in a single-polarization state, suppressing polarization noise. We successfully fabricated a Si 3 N 4 resonator with a bending radius of 17.5 mm, a finesse ( F ) of 150, a quality factor ( Q ) of 1.54 × 10 7 , and a propagation loss of 1.2 dB/m. The Si 3 N 4 resonator was used to construct a double closed-loop RIOG that showed long-term bias stability (3600 s) of 13.2°/h at room temperature, 14.8°/h at 40°C, 21.2°/h at 50°C, and 23.6°/h at 60°C. We believe this to be the best performance reported to date for a Si 3 N 4 resonator-based RIOG. This advancement paves the way for the wider application of RIOGs.

Quantum state interferography with heralded single photons

Quantum state tomography is the standard method used for quantum state reconstruction. Recently, a new technique called, quantum state interferography, has been introduced for the direct single-shot measurement of the quantum state of a qubit [Phys. Rev. Lett. 125 (2020) 123601]. In the present work, we report a first-of-its-kind experimental demonstration of quantum state interferography of legitimate single photon polarization states derived from spontaneous parametric down conversion source. Further, we provide a more general and a simpler mathematical treatment of the QSI technique. While the theoretical treatment with d-dimensional state vectors in the earlier work is limited only to pure qudits, our approach readily lends itself to the case of mixed qudit systems. The basic arguments and the results of this extension are presented with a qutrit state as an example.

Polarization‐controlled VCSEL characterization

AbstractMost VCSELs are not designed to emit in a single polarization state and often there is no control over the polarization angle. A novel one‐shot method measures the spatial polarization of each single emitter and allows to correct the polarization dependency of the setup. This process minimizes the error budget of the VCSEL testing system and measures accurate values for laser eye safety calculations.

Structure of Chern-Simons scattering amplitudes from topological equivalence theorem and double-copy

We study the mechanism of topological mass-generation for 3d Chern-Simons (CS) gauge theories, where the CS term can retain the gauge symmetry and make gauge boson topologically massive. Without CS term the 3d massless gauge boson has a single physical transverse polarization state, while adding the CS term converts it into a massive physical polarization state and conserves the total physical degrees of freedom. We formulate the mechanism of topological mass-generation at S-matrix level. For this, we propose and prove a Topological Equivalence Theorem (TET) which connects the N-point scattering amplitude of the gauge boson’s physical polarization states ( {A}_{mathrm{P}}^a ) to that of the transverse polarization states ( {A}_{mathrm{T}}^a ) under high energy expansion. We present a general 3d power counting method on the leading energy dependence of the scattering amplitudes in both topologically massive Yang-Mills (TMYM) and topologically massive gravity (TMG) theories. With these, we uncover a general energy cancellation mechanism for N -gauge boson scattering amplitudes which predicts the cancellation E4→ E4−N at tree level. Then, we compute the 4-gauge boson amplitudes of {A}_{mathrm{P}}^a -states and {A}_{mathrm{T}}^a -states, with which we explicitly demonstrate the TET and establish such energy cancellations for N = 4. We further extend the double-copy approach to reconstruct the massive 4-graviton amplitude of TMG from the massive 4-gauge boson amplitude of TMYM. With these, we uncover striking large energy cancellations in the 4-graviton amplitude: E12→ E1, and establish its correspondence to the leading energy cancellation E4→ E0in the 4-gauge boson amplitude of TMYM.

Resonant integrated optical gyroscope based on Si3N4 waveguide ring resonator

A resonant integrated optical gyroscope (RIOG) based on silicon nitride (Si3N4) waveguide ring resonator (WRR) with single-polarization performance is proposed and demonstrated. The Si3N4 WRR has high polarization-dependent loss and can maintain a single polarization state, thereby avoiding other polarization modes from affecting the performance of the RIOG. In this paper, we design and fabricate a Si3N4 WRR with a bending radius of 8 mm, which shows excellent single-polarization performance is demonstrated at different temperatures. Finally, a long-term bias stability (3600s) of 0.68°/s in an integration time of 164s are successfully demonstrated. To the best of our knowledge, this is the first reported to date for the Si3N4 WRR-based RIOG.

Polarization sensitive optical coherence tomography with single input for imaging depth-resolved collagen organizations

Collagen organization plays an important role in maintaining structural integrity and determining tissue function. Polarization-sensitive optical coherence tomography (PSOCT) is a promising noninvasive three-dimensional imaging tool for mapping collagen organization in vivo. While PSOCT systems with multiple polarization inputs have demonstrated the ability to visualize depth-resolved collagen organization, systems, which use a single input polarization state have not yet demonstrated sufficient reconstruction quality. Herein we describe a PSOCT based polarization state transmission model that reveals the depth-dependent polarization state evolution of light backscattered within a birefringent sample. Based on this model, we propose a polarization state tracing method that relies on a discrete differential geometric analysis of the evolution of the polarization state in depth along the Poincare sphere for depth-resolved birefringent imaging using only one single input polarization state. We demonstrate the ability of this method to visualize depth-resolved myocardial architecture in both healthy and infarcted rodent hearts (ex vivo) and collagen structures responsible for skin tension lines at various anatomical locations on the face of a healthy human volunteer (in vivo).

Tunable and enhanced performance of graphene-assisted plasmonic sensor with photonic spin Hall effect in near infrared: analysis founded on graphene’s chemical potential and components of light polarization

In this work, we propose a graphene-assisted plasmonic structure with photonic spin Hall effect (PSHE) for sensing applications in near infrared with an emphasis on tunable and spin control aspects leading to enhanced performance. We comprehensively investigate PSHE in view of variable chemical doping of graphene monolayer in the structure and manipulation of the spin dependent splitting by considering single and cross polarization states. There is observed a considerable variation in spin shift due to increase in chemical potential or Pauli blocking, which fundamentally controls the light absorption by graphene. Our simulation results reveal that the amplified spin dependent shift (SDS) is 1.13 × 104 times higher than the conventional SDS at 0.436 eV of graphene chemical potential. Further, this structure is utilised for sensing application, and it is observed that graphene-assisted plasmonic based structure possesses significantly greater spin dependent sensitivity (5.53 times), figure of merit (8.56 × 105 times), and extremely finer limit of detection (by a factor of 18.10) are achieved compared to the structure without graphene. The results indicate that choosing the proposed graphene-assisted plasmonic structure with variable chemical potential and light polarization components, an extremely enhanced sensing performance can be achieved. The results are consistent with the physical rationale and are particularly important for potential biosensing applications.

Single-mode lasers using parity-time-symmetric polarization eigenstates

Anisotropic mirrors are used to form a laser resonator exhibiting non-Hermitian, parity-time (PT) symmetric, polarization states. The relative angle of the two mirrors principal axes is used to control the degree of non-hermiticity. A sharp symmetry-breaking transition is observed at a specific angle, called the exceptional point, where the two states coalesce into a single polarization state and the interference pattern produced by counter-propagating (CP) waves vanishes. At a smaller angle, in the unbroken PT symmetry regime, the polarization state experiencing higher losses is suppressed. In the broken symmetry regime, the two polarization states coexist, but the orthogonality of the CP waves favors single longitudinal mode emission by suppressing the interference pattern of the standing wave. The two regimes meet at the exceptional point, where a unique polarization state exists in a resonator free from interference intensity pattern. Microchip PT-symmetric lasers operating at the exceptional point are thus an attractive solution to achieve single mode operation from a miniature monolithic device without any intra-cavity element.

Generation of Pure OAM Beams with a Single State of Polarization by Antenna-Decorated Microdisk Resonators

We report waveguide-addressed plasmonic-photonic resonators that generate beams of controlled orbital angular momentum and spin angular momentum content upon driving through a waveguide. From phase-gradient metasurfaces, we borrow the idea of carefully combining multiple nanoscale resonators in a repeat unit, from which we build periodic rings that decorate microdisk resonators. We describe the general mode structure of microdisk cavities perturbed by antenna arrays on the basis of a quasinormal mode formalism and present a strategy to simultaneously control the orbital and spin angular momentum content of light outcoupled to the far field. We propose a realization that uses silicon nitride disks and aluminum nanorod antennas. We find excellent polarization and orbital angular momentum (OAM) purity, as benchmarked by polarization-resolved interferometric Fourier microscopy on single devices.

Deep Learning-Based Holographic Polarization Microscopy.

Polarized light microscopy provides high contrast to birefringent specimen and is widely used as a diagnostic tool in pathology. However, polarization microscopy systems typically operate by analyzing images collected from two or more light paths in different states of polarization, which lead to relatively complex optical designs, high system costs, or experienced technicians being required. Here, we present a deep learning-based holographic polarization microscope that is capable of obtaining quantitative birefringence retardance and orientation information of specimen from a phase-recovered hologram, while only requiring the addition of one polarizer/analyzer pair to an inline lensfree holographic imaging system. Using a deep neural network, the reconstructed holographic images from a single state of polarization can be transformed into images equivalent to those captured using a single-shot computational polarized light microscope (SCPLM). Our analysis shows that a trained deep neural network can extract the birefringence information using both the sample specific morphological features as well as the holographic amplitude and phase distribution. To demonstrate the efficacy of this method, we tested it by imaging various birefringent samples including, for example, monosodium urate and triamcinolone acetonide crystals. Our method achieves similar results to SCPLM both qualitatively and quantitatively, and due to its simpler optical design and significantly larger field-of-view this method has the potential to expand the access to polarization microscopy and its use for medical diagnosis in resource limited settings.

Reciprocity-induced symmetry in the round-trip transmission through complex systems.

Reciprocity is a fundamental principle of wave physics and directly relates to the symmetry in the transmission through a system when interchanging the input and output. The coherent transmission matrix (TM) is a convenient method to characterize wave transmission through general media. Here, we demonstrate the optical reciprocal nature of complex media by exploring their TM properties. We measured phase-corrected TMs of forward and round-trip propagation in a single polarization state through a looped 1 m-long step-index optical multimode fiber (MMF) to experimentally verify a transpose relationship between the forward and backward transmission. This symmetry impedes straightforward MMF calibration from proximal measurements of the round-trip TM. Furthermore, we show how focusing through the MMF with digital optical phase conjugation is compromised by system loss since time reversibility relies on power conservation. These insights may inform the development of new imaging techniques through complex media and coherent control of waves in photonic systems.

Microwave Study of a Solar Circular Ribbon Flare

Abstract A circular ribbon flare (CRF) SOL2014-12-17T04:51 is studied using the 17/34 GHz maps from the Nobeyama Radioheliograph along with (E)UV and magnetic data from the Solar Dynamics Observatory. We report the following three findings as important features of the microwave CRF. (1) The first preflare activation comes in the form of a gradual increase of the 17 GHz flux without a counterpart at 34 GHz, which indicates thermal preheating. The first sign of nonthermal activity occurs in the form of stepwise flux increases at both 17 and 34 GHz about 4 minutes before the impulsive phase. (2) Until the impulsive phase, the microwave emission over the entire active region is in a single polarization state matching the magnetic polarity of the surrounding fields. During and after the impulsive phase, the sign of the 17 GHz polarization state reverses in the core region, which implies a magnetic breakout–type eruption in a fan–spine magnetic structure. (3) The 17 GHz flux around the time of the eruption shows quasi-periodic variations with periods of 1–2 minutes. The pre-eruption oscillation is more obvious in total intensity at one end of the flare loop, and the post-eruption oscillation, more obvious in the polarized intensity at a region near the inner spine. We interpret this transition as transfer of oscillatory power from kink mode oscillation to torsional Alfvén waves propagating along the spine field after the eruption. We argue that these three processes are interrelated and indicate a breakout process in a fan–spine structure.

High-power and single-mode VCSEL arrays with single-polarized outputs by using package-induced tensile strain.

In this work, we demonstrate a novel high-power vertical-cavity surface-emitting laser (VCSEL) array with highly single-mode (SM) and single-polarized output performance without significantly increasing the intra-cavity loss and threshold current (Ith). By combining a low-loss zinc-diffusion aperture with an electroplated copper substrate, we can obtain a highly SM output (side mode suppression ratio >50dB) with a very narrow divergence angle (1/e2:∼10∘) under high output power (3.1 W; 1% duty cycle) and sustain a single polarization state, with a polarization suppression ratio of around 9 dB, under the full range of bias currents. Compared to the reference device without the copper substrate, the demonstrated array can not only switch the output optical spectra from quasi-SM to highly SM but also maintain a close threshold current value (Ith: 0.8 versus 0.7 mA per unit device) and slope efficiency. The enhancement in fundamental mode selectivity of our VCSEL structure can be attributed to the single-polarized lasing mode induced by tensile strain, which is caused by the electroplated copper substrate, as verified by the double-crystal x-ray measurement results.